Nonlinear, fractal, and spectral analysis of the EEG of lizard,Gallotia galloti

Abstract

Electroencephalogram (EEG) from dorsal cortex of lizard Gallotia galloti was analyzed at different temperatures to test the presence of fractal or nonlinear structure during open (OE) and closed eyes (CE), with the aim of comparing these results with those reported for human slow-wave sleep (SWS). Two nonlinear parameters characterizing EEG complexity [correlation dimension (D2)] and predictability [largest Lyapunov exponent (λ1)] were calculated, and EEG spectrum and fractal exponent β were determined via coarse graining spectral analysis. At 25°C, evidence of nonlinear structure was obtained by the surrogate data test, with EEG phase space structure suggesting the presence of deterministic chaos (D2 ∼6, λ1 ∼1.5). Both nonlinear parameters were greater in OE than in CE and for the right hemisphere in both situations. At 35°C the evidence of nonlinearity was not conclusive and differences between states disappeared, whereas interhemispheric differences remained for λ1. Harmonic power always increased with temperature within the band 8–30 Hz, but only with OE within the band 0.3–7.5 Hz. Qualitative similarities found between lizard and human SWS EEG support the hypothesis that reptilian waking could evolve into mammalian SWS.

Motivation, emotion, and their inhibitory control mirrored in brain oscillations

“…Oscillations of delta, theta, and alpha ranges could be found in all vertebrates but there is an important distinction between reptiles, lower mammals and humans in what frequency dominates in the scalp EEG. Alpha is the dominant frequency in adult humans, while theta dominates in the EEG of lower mammals (Sainsbury, 1998) and delta in the reptilian EEG (Gaztelu et al, 1991;Gonzalez et al, 1999). Given the above-discussed functional correlates of the three oscillatory systems, this fact may indicate that the behavior of lower vertebrates more depends on internal motivational drives associated with delta oscillations; the behavior of lower mammals is more determined by emotional reactions and emotional learning which are linked with theta activity; the human behavior more relies on the processes and functions associated with alpha oscillations.…”

Alpha oscillations as a correlate of trait anxiety

“…But there is an important distinction between reptiles, lower mammals, and humans in what frequency dominates in the scalp EEG. Alpha is the dominant frequency in adult humans, while theta dominates in the EEG of lower mammals (Klimesch, 1999) and delta in the reptilian EEG (Gaztelu et al, 1991;Gonzalez et al, 1999). That means that all three oscillatory systems were acquired early in the evolution of vertebrates, but they further developed with different rates.…”

Unraveling the complexities of circadian and sleep interactions with memory formation through invertebrate research

“…Despite the similarities in the two stage sleep state of these groups, the emergence of REM and NREM sleep appears to be through convergent evolution (Rattenborg, 2007; Rattenborg et al, 2012). In aquatic mammals, reptiles, amphibians and other vertebrates, slow wave sleep has been consistently detected although REM sleep is not always present (Hobson et al, 1968; Mukhametov et al, 1977; González et al, 1999) reviewed in Williams et al (1973) and Madan and Jha (2012). Monotremes, such as the echidna and platypus, demonstrate a single sleep state that shows characteristics of both slow wave and REM sleep (Siegel et al, 1996, 1998, 1999; Nicol et al, 2000).…”